With the advancement in technologies, servo motor control has played an important role in both traditional and high-tech industries. As the chip design techniques have been improved, it is a trend to develop servo motor control towards high precision. To implement high-precision control, the standard for the servo control chip performance as well as the encoder resolution is high. However, the commercially available servo control chips and encoders may not be satisfactory, which leads to higher cost if application specific ICs (ASIC) are required. Therefore, to reduce the cost, the existing servo control chip and encoder can be used with a method capable of improving the driving capability of the servo control chip. Such a method has to be compatible with the interface of the existing servo control chip and capable of enhance the resolution of the encoder. Moreover, the method has to be resistant to the environmental noise or capable of de-noising because the servo driver is often installed in a place more severe than in a general labrotory.
The low-resolution communication format for an encoder is the parallel communication, while the high-resolution communication format is the serial communication using a different pin count. Moreover, the commercially available servo control chip sold with the encoder only supports the parallel communication. Therefore, the commercially available servo control chip does not provide the pin count to support the high-resolution serial communication. Accordingly, the performance of the servo driver is limited by the resolution of the encoder. Even though the commercially available servo control chip can be used to achieve high-precision control, it still fails to meet the specifications of the high-performance of a servo driver. If the commercially available servo control chip is required to support the data receiving from the high-resolution encoder, a specially designed servo control chip is required to increase the cost. If the specially designed servo control chip is not used, the servo control chip of the servo driver has to support the communication format and pin design of the high-resolution encoder, which leads to higher cost.
Generally, a deceleration mechanism is used to achieve low speed output if the high-resolution encoder is not used. With the use of the deceleration mechanism, the overall size of the servo motor mechanism will be significantly enlarged to increase the cost and shorten the lifetime of the deceleration mechanism. Accordingly, the mechanism has to be fixed and/or replaced regularly to increase the cost. Moreover, with the use of the deceleration mechanism, the shifting from high to low gears may not be smooth. Therefore, economical benefit appears if high speed/control ratio is achieved without using the deceleration mechanism; and significant economical benefit appears if high speed/control ratio is achieved by the use of the low-resolution encoder.
Please refer to U.S. Pat. No. 6,556,131, which shows a schematic diagram of a conventional low speed control structure of a servo motor. The output signal from the position senser of the servo motor is sinusoidal, which is processed by an analog-to-digital converter (ADC) chip to output the position of the servo motor. U.S. Pat. No. 6,556,131 uses the output data from the ADC chip to calculate the position of the servo motor by comparing with the look-up table according to the speed of the servo motor. The encoder resolution is not fixed but determined according to the number of the processing speed of the processor and the number of processed bits.
In the present invention, the commercially available encoder is used. The resolution is increased by the method of the present invention to transmit data to the servo control chip. The present invention is similar to the prior art in that the resolution of the servo motor position is improved. However, in the prior art, the sinusoidal signal from the position senser of the servo motor is processed by an analog-to-digital converter (ADC) chip. The resolution of the servo motor depends on the number of bits of the ADC chip and the number of bits of the encoder.